Impulse radio ultra-wideband (IR-UWB) enables precise ranging and location estimation due to extremely fast and short duration pulses, e.g., billions of sub-nanosecond pulses per second. Accurate time-of-arrival (TOA) estimation of the received signal is a key aspect for precise ranging. However, received UWB signals can include hundreds of multipath components, which increase the difficulty of TOA estimation.
If a coarse timing estimate is available, then an energy of the received samples can be compared with an energy threshold. The first sample that exceeds the threshold can be used as an estimate of the TOA.
However, it is a problem to select an appropriate threshold. The threshold can be based on received signal statistics, i.e., the signal-to-noise ratio (SNR) or a channel realization. If the selected threshold is based solely on noise variance, then the variance of the noise needs to be determined, Scholtz et al., “Problems in modeling UWB channels,” Proc. IEEE Asilomar Conf. Signals, Syst. Computers, vol. 1, pp. 706-711, November 2002.
One method uses a normalized threshold technique that assigns a threshold between minimum and maximum values of energy samples, see U.S. patent application Ser. No. 11/995,394 entitled “Method and Receiver for Identifying a Leading Edge Time Period in a Received Radio Signal” and filed by Molisch et al. on Jan. 11, 2008. However, there are two practical limitations to that method. It is difficult to estimate the SNR, and using only the SNR of the received signal does not account for individual channel realizations. This results in a suboptimal threshold selection.